1. Field of the Invention
The invention relates generally to cross-linked polymers and in particular to polymer precursor compositions, and polymers, thermosets and ceramics made by reacting silyl/siloxyl substituted carboranes having unsaturated organic end groups with hydrosilanes and hydrosiloxanes.
2. Description of the Related Art
The search for high temperature oxidatively stable materials has led to the development of organoboron polymers, particularly silyl or siloxyl polymers containing carboranyl and acetylenic groups incorporated into the polymer backbone. Polymers that include carboranyl, silyl or siloxyl and acetylenic groups in the same polymeric chain combine the desirable features of both inorganics and organics: the carborane groups provide thermal and oxidative stability, the silane or siloxane groups provide chain flexibility and the acetylenic groups allow cross-linking of adjacent polymer strands to form thermosets. The acetylene groups remain inactive during processing at lower temperatures and react either thermally or photochemically to form conjugated polymeric cross-links without the evolution of volatiles. Carborane-silane/siloxane-acetylene polymers have the advantage of being extremely easy to process and convert into thermosets or ceramics since they are either liquids at room temperature or low melting solids and are soluble in most organic solvents. The polymers are thus well-suited to serve as ceramic or thermoset polymeric precursors.
Thermoset polymers that include carborane, silane or siloxane and acetylene units are disclosed in U.S. Pat. No. 5,272,237; U.S. Pat. No. 5,292,779; U.S. Pat. No. 5,348,917; U.S. Pat. No. 5,483,017, and U.S. Pat. No. 5,681,870, each incorporated herein by reference in its entirety and for all purposes. The thermoset polymers described in U.S. Pat. Nos. 5,272,237; 5,292,779 and 5,348,917 are made from linear polymer precursors that include repeating units containing carborane-silane/siloxane-acetylene or related groups. The thermoset polymers described in U.S. Pat. No. 5,483,017 are made from linear polymer precursors that include, on each strand, both repeating units of carborane-silane/siloxane-acetylene or related groups and repeating units of siloxane/silane-acetylene or related groups. U.S. Pat. No. 5,681,870 describes a linear polymer with randomly distributed carborane, silane/siloxane and acetylene units. U.S. Pat No. 5,348,917, U.S. Pat. No. 5,483,017 and U.S. Pat. No. 5,681,870 further disclose boron-arbonsilicon ceramics made by pyrolyzing carborane-silane/siloxane-acetylene thermoset polymers.
While these polymers show outstanding thermal and thermo-oxidative stabilities, their use is limited due to the high cost and limited availability of carboranes and the high cost of dilithiated acetylenes used in making the polymers.
U.S. Pat. No. 5,679,818, incorporated herein by reference, describes compounds of the formula R.sup.1 --Ac.sup.1 --Ar.sup.1 --M--Ar.sup.2 --Ac.sup.2 --R.sup.2, wherein M is a silyl/siloxyl substituted carborane, Ar.sup.1 and Ar.sup.2 are aromatic groups, and Ac.sup.1 and Ac.sup.2 are alkynyl groups. The compounds are described as being useful as precursors for thermosets. Synthesis of these compounds involves the steps of attaching aromatic groups Ar.sup.1 and Ar.sup.2 to the silyl/siloxyl group and then attaching the alkynyl-containing groups R.sup.1 --Ac.sup.1 -- and R.sup.2 --Ac.sup.2 -- to the aromatic groups.